The Bible does mention at least one instance where a woman was not given to a younger man, but this was a case of Levirate marriage (Genesis 38) and nothing is said about the rightness or wrongness of the age difference.
A younger woman marrying an older man is convention, not a rule of any kind. It likely stems from the fact that females generally mature physically at an earlier age than males, so young females on the lookout are naturally looking to slightly older males.
I'm curious what prompted the OP question.